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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 24 July 2011 by John Hartz

This article is a re-post of a Universtiy of Arizona news release by Daniel Stolte, University Communications.

If sea levels rose to where they were during Last Interglacial Period, large parts of the Gulf of Mexico region would be under water (red areas), including half of Florida and several Caribbean islands. (Photo illustration by Jeremy Weiss)

Melting ice sheets contributed much more to rising sea levels than thermal expansion of warming ocean waters during the Last Interglacial Period, a UA-led team of researchers has found. The results further suggest that ocean levels continue to rise long after warming of the atmosphere levels off.

Thermal expansion of seawater contributed only slightly to rising sea levels compared to melting ice sheets during the Last Interglacial Period, a University of Arizona-led team of researchers has found.

The study combined paleoclimate records with computer simulations of atmosphere-ocean interactions and the team's co-authored paper is accepted for publication in Geophysical Research Letters.

As the world's climate becomes warmer due to increased greenhouse gases in the atmosphere, sea levels are expected to rise by up to three feet by the end of this century.

But the question remains: How much of that will be due to ice sheets melting as opposed to the oceans' 332 million cubic miles of water increasing in volume as they warm up?

For the study, UA team members analyzed paleoceanic records of global distribution of sea surface temperatures of the warmest 5,000-year period during the Last Interglacial, a warm period that lasted from 130,000 to 120,000 years ago.

The researchers then compared the data to results of computer-based climate models simulating ocean temperatures during a 200-year snapshot as if taken 125,000 years ago and calculating the contributions from thermal expansion of sea water.

The team found that thermal expansion could have contributed no more than 40 centimeters – less than 1.5 feet – to the rising sea levels during that time, which exceeded today's level up to eight meters or 26 feet.

At the same time, the paleoclimate data revealed average ocean temperatures that were only about 0.7 degrees Celsius, or 1.3 degrees Fahrenheit, above those of today.

"This means that even small amounts of warming may have committed us to more ice sheet melting than we previously thought. The temperature during that time of high sea levels wasn't that much warmer than it is today," said Nicholas McKay, a doctoral student at the UA's department of geosciences and the paper's lead author.

McKay pointed out that even if ocean levels rose to similar heights as during the Last Interglacial, they would do so at a rate of up to three feet per century.

"Even though the oceans are absorbing a good deal of the total global warming, the atmosphere is warming faster than the oceans," McKay added. "Moreover, ocean warming is lagging behind the warming of the atmosphere. The melting of large polar ice sheets lags even farther behind."

"As a result, even if we stopped greenhouse gas emissions right now, the Earth would keep warming, the oceans would keep warming, the ice sheets would keep shrinking, and sea levels would keep rising for a long time," he explained.

They are absorbing most of that heat, but they lag behind. Especially the large ice sheets are not in equilibrium with global climate," McKay added. "

Jonathan Overpeck, co-director of the UA's Institute of the Environment and a professor with joint appointments in the department of geosciences and atmospheric sciences, said: "This study marks the strongest case yet made that humans – by warming the atmosphere and oceans – are pushing the Earth's climate toward the threshold where we will likely be committed to four to six or even more meters of sea level rise in coming centuries."

Overpeck, who is McKay's doctoral advisor and a co-author of the study, added: "Unless we dramatically curb global warming, we are in for centuries of sea level rise at a rate of up to three feet per century, with the bulk of the water coming from the melting of the great polar ice sheets – both the Greenland and Antarctic Ice Sheets."

According to the authors, the new results imply that 4.1 to 5.8 meters, or 13.5 to 19 feet, of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet, "reemphasizing the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to warming temperatures than widely thought."

"The central question we asked was, ‘What are the warmest 5,000 years we can find for all these records, and what was the corresponding sea level rise during that time?'" McKay said.

Evidence for elevated sea levels is scattered all around the globe, he added. On Barbados and the Bahamas, for example, notches cut by waves into the rock six or more meters above the present shoreline have been dated to being 125,000 years old.

"Based on previous studies, we know that the sea level during the Last Interglacial was up to 8.5 meters higher than today," McKay explained.

"We already knew that the vast majority came from the melting of the large ice sheets in Greenland and Antarctica, but how much could the expansion of seawater have added to that?"

Given that sea surface temperatures were about 0.7 degrees warmer than today, the team calculated that even if the warmer temperatures reached all the way down to 2,000 meters depth – more than 6,500 feet, which is highly unlikely – expansion would have accounted for no more than 40 centimeters, less than a foot and a half.

"That means almost all of the substantial sea level rise in the Last Interglacial must have come from the large ice sheets, with only a small contribution from melted mountain glaciers and small ice caps," McKay said.

"The models allow us to attribute changes we observe in the paleoclimate record to the physical mechanisms that caused those changes," Otto-Bliesner said. "This helps tremendously in being able to distinguish mere correlations from cause-and-effect relationships."

The authors cautioned that past evidence is not a prediction of the future, mostly because global temperatures during the Last Interglacial were driven by changes in the Earth's orbit around the sun. However, current global warming is driven by increasing greenhouse gas concentrations.

The seasonal differences between the northern and the southern hemispheres were more pronounced during the Last Interglacial than they will be in the future.

"We expect something quite different for the future because we're not changing things seasonally, we're warming the globe in all seasons," McKay said.

"The question is, when we think about warming on a global scale and contemplate letting the climate system change to a new warmer state, what would we expect for the ice sheets and sea levels based on the paleoclimate record? The Last Interglacial is the most recent time when sea levels were much higher and it's a time for which we have lots of data," McKay added.

"The message is that the last time glaciers and ice sheets melted, sea levels rose by more than eight meters. Much of the world's population lives relatively close to sea level. This is going to have huge impacts, especially on poor countries," he added.

"If you live a meter above sea level, it's irrelevant what causes the rise. Whether sea levels are rising for natural reasons or for anthropogenic reasons, you're still going to be under water sooner or later."

Comments

A foot rise of sea level along the Connecticut coast would prove very costly. Most of the states public parks would be in deep trouble. 1 foot rise would leave Rocky Neck state park http://www.ct.gov/dep/cwp/view.asp?a=2716&q=325256 and Hammonasset Beach State Park, http://www.ct.gov/dep/cwp/view.asp?a=2716&q=325210 Both In deep trouble. Both beaches are now suffering from severe erosion.

The cities of New London & Groton (home of the US Sub Base) would face serious flooding during storms. With New London seeing permanent sections under water.

New Haven, home to Yale would see flooding from winter storms and sewage problems.

Bridgeport would see its deep water port extend into downtown!! With 2 feet of sea rise- possible by 2050. the costs for mitigating this are exponential. Yet we have many in the US Congress fighting over the chump change deficits we have now. Power in the hands of fools.

I disagree with a lot in this paper. Mainly, I don't agree with how they arrived at their figures. If we take empirical data maintained by the University of Colorado, and do some simple math, we get the following (I will even use the upper range).

UA team members analyzed paleoceanic records of global distribution of sea surface temperatures ... then compared the data to results of computer-based climate models simulating ocean temperatures ... The team found that thermal expansion could have contributed no more than 40 centimeters – less than 1.5 feet – to the rising sea levels during that time ... That means almost all of the substantial sea level rise in the Last Interglacial must have come from the large ice sheets

For the dissenting 'study,' we see a graph covering an 18 year period and an extrapolation to 89 years.

aPirate, according to your method, Mt. Everest will be under water in roughly 2.78 million years. Trends are inherently historical. Models are used for prediction. How do you justify using such a simple model (extending the trend line) to predict such a complex event?

Arguing from an extended trend line is useless. Get a better analysis--preferably one based in physics (unless your physical model actually predicts the second coming of Noah; if so, that would explain a lot about some of the arguments you've made).

Back in the early 50's, a group of scientists had predicted that sea levels would rise higher than the predictions made by the IPCC 50 years later.
Their analysis then was because we are at the end of interglacial period.
I don't remember there being any type of hysteria then as opposed to now.
Only now though, it's frightening and catastrophic because its man-made.
What interesting times we live in.

"McKay pointed out that even if ocean levels rose to similar heights as during the Last Interglacial, they would do so at a rate of up to three feet per century."

err ... how does he come by this. I think he means average rate. The rate is by no means going to be steady. There are documented cases of large SLR over short time scales. Our CO2 forcing is ballistic compared to interglacial ones so I would think we will see spectacular ice collapse maybe sooner than later...

"Even though the oceans are absorbing a good deal of the total global warming, the atmosphere is warming faster than the oceans," McKay added. "Moreover, ocean warming is lagging behind the warming of the atmosphere. The melting of large polar ice sheets lags even farther behind."

I have seen graphs on this site indicating that most of the warming went in to the ocean. So am a bit confused by this statement.....

"We expect something quite different for the future because we're not changing things seasonally, we're warming the globe in all seasons," McKay said."

Surely the main forcing once warming got underway was GHGs which reenforced the seasonal warming and at some point takes over. Would be interesting to find this point where the ghg feedback takes over from orbital forcing....

apirate @12, the IPCC projections are not linear, and explicitly exclude melt water from glaciers because they are not sufficiently predictable. Those glaciers will melt, however, or at least a significant amount of the Greenland Ice Sheet and the West Antarctic Ice Sheet will melt although it will probably take centuries to do so.

Based on your second graph (from wikipedia, I believe) the sea level rose 115 meters in the 8 thousand years from 16k before present to 8 k before present. That represents a rate of rise of 144 mm/decade, and is a reasonable projection for the rate of rise by the end of this century. That would yield a sea level rise in the order of 650 mm by 2100, and double that for the following centuries until the 6 to 8.5 meter rise above current levels is achieved, assuming we restrict GHG emissions sufficiently to restrict global temperature increases to 2 degrees C.

Contrary to many commentators here, I believe that those rates are well withing the economic means for adaption; but I also think sea level rise will cause the least economic hardship globally of the various risks from global warming.

Whether sea level showed 20th-century acceleration or not, it’s the century coming up which is of concern. And during this century, we expect acceleration of sea level rise because of physics. Not only will there likely be nonlinear response to thermal expansion of the oceans, when the ice sheets become major contributors to sea level rise, they will dominate the equation. Their impact could be tremendous, it could be sudden, and it could be horrible.

@Composer99
A citation wouldn't be necessary if those that said they were knowledgeable of facts, were actually knowledgeable of the facts.

Dr. George F. Carter was quoted as saying, “Sea level the whole world over is five inches higher. Because this is the tail end of a glacial period, polar ice is melting and filling up the oceans. Future harbor works should be planned for an expected sea level rise of 24 inches within the next century.”

This quote and another like can be found in Popular Mechanics Mar'53 and Popular Science Feb.'53.

George F. Carter taught at John Hopkins University as acting chair of the Geography Dept., and at Texas A&M as Distinguished Professor of Geography.

Before he taught at John Hopkins, he served as an analyst for the Office of Strategic Services(better known as the C.I.A.), during WWII.

Two papers worth reviewing his extensive work are:

EARLY MAN AT SAN DIEGO: A GEOMORPHIC·ARCHAEOLOGICAL VIEW
&
MAN, TIME, & CHANGE IN THE FAR SOUTHWEST.

Or, if you like, there are many reviews of his works on geography/anthropology.

If he was alive today, he would probably tell you that he was a climatologist as well.

In his work, he used sediment readings from many parts of the world and had concluded that there have been at least 2 interglacial periods before this current one and that seas had risen 100s of feet before, and quite likely, will do so again.

Dr. Carter had even mentioned that without some sort of relapse(cooling), that the seas could repeat the process again, possibly in our lifetime or our children's lifetime.

Dr. Carter passed away in 2004.
He will be missed.

00

Response:

[DB] "A citation wouldn't be necessary if those that said they were knowledgeable of facts, were actually knowledgeable of the facts."

"There is considerable variability in the rate of rise during the twentieth century but there has been a statistically signiﬁcant acceleration since 1880 and 1900 of 0.009 ± 0.003 mm year and 0.009 ± 0.004 mm year-2 , respectively. Since the start of the altimeter record in 1993, global average sea level rose at a rate near the upper end of the sea level projections of the Intergovernmental Panel on Climate Change’s Third and Fourth Assessment Reports"

And to illustrate the point about IPCC sea level projections and actual observations (your last graphic isn't clear enough):

Actual sea level rise is tracking the upper bound of projections.

Pirate - "So, whether we look at 18 years, 120 years, or 8,000 years we are seeing a linear response."

A one paragraph prediction in Popular Science (repeated in Popular Mechanics) by someone who was mostly an anthropologist is supposed to be well known to people discussing climate science? Where is there any indication this prediction was ever reported beyond this cite?

And your quote is incomplete. Here is the full one (which your link actually provided in full):

"Sea level the whole world over is five inches higher than it was in 1895, says Dr. George F Carter, Johns Hopkins University geographer. Because this is the tail end of a glacial period, polar ice is melting and filling up the oceans. Future harbor works should be planned for an expected sea level rise of 24 inches within the next century, Dr. Carter advises"

And it should be noted he's just wrong; sea level was not rising because "this is the tail end of a glacial period". We have been in the middle of an interglacial for thousands of years. If he meant the "Little Ice Age", he would still have to provide a physical reason for why sea level started rising; it didn't start rising because it had been colder before. Sea level had been rising because of a combination of increased solar irradiance and rising GHG's warmed the Earth. Since the middle of the 20th century, the warming has been primarily from GHG's.

The musings of someone without a lot of background in sea level rise speaking at a time when that science was in its infancy, and quoted in 2 magazines for laymen has no relevance to the science as it is now. Why bring him up? His prediction had no influence.

This international scientific assessment has been carried out at the request of the Dutch Delta Committee. The Committee requested that the assessment explore the high-end climate change scenarios for flood protection of the Netherlands. It is a state-of–the art scientific assessment of the upper bound values and longer term projections (for sea level rise up to 2200) of climate induced sea level rise, changing storm surge conditions and peak discharge of river Rhine. It comprises a review of recent studies, model projections and expert opinions of more than 20 leading climate scientists from different countries around the North Sea, Australia and the USA. Although building on the previous IPCC AR4 (2007) and KNMI (2006) assessments, this report deliberately explores low probability/high impact scenarios, which will pose significant threats to the safety of people and infrastructure and capital invested below sea level. According to its high-end estimates global mean sea level may rise in the range of 0.55 - 1.10 m in 2100 and 1.5 - 3.5 m in 2200, when higher temperature rise scenarios (up to 6 °C by 2100) and increased ice discharge from Antarctica are considered. This would correspond with local sea levels along the coast of the Netherlands of up to maximally 1.20 m in 2100 and 4 m in 2200. An increase in peak discharge of river Rhine of 3 to 19% for 2050 and 6 to 38% for 2100 is foreseen. The storm regime along the Dutch North Sea coast in terms of maximum surge level will probably not change significantly in this extreme climate change frame.

#20 Bad,
Yes, but peer review information is now coming out indicating that, especially if we dont reduce our rate of emission, but even if we do, that we might (could) get 5-6ft by around 2100. And then it will keep going up and up.... They take about 6ºC giving 4ms, but we can see in this article (& from Hansen) that a 1ºC rise from now will result in a 8m rise at some point.

What this article shows also is that it is not stopping there, but will continue on to around 20ft+ even if we do stop our emissions as there is at least .7ºC in the pipeline and probably more.

We also have to get back to around 350ppm and below before we see equilibrium (Hansen).

It really does not make sense for the Netherlands to spend billions and billons to defend when they will have to retreat. That money could be better spent. This reality has to enter the debate now.

Nothing is certain, but this is looking more and more certain with each year! And the current data should cause pause for re-review of strategy I would guess considering the cost.

There was a public meeting here about sealevel rise and it's threat to the city (which has some immediate issues) with contributions from surveyors, engineers, town planners etc. One very good point that an engineer made was that scope and affordability of engineering solutions was inversely proportional to total expected sea level rise. If the rise is around 1m, then engineering is possible and effective. If it is 2-3m then retreat is only realistic option.

What will be the effect of the rising pressure of the sea on the lower agricultural grounds? Will the salt water level rise to an extend that it is not usable any-more? Seems to me especially a problem from Zeeland and Noord-Holland provinces in the Netherlands AND for large delta areas. It can be that rising water levels in rivers will counter the effect. For rivers already locked in by dykes that effect will be less.

Although additional investment in flood and erosion protection will be considerable (estimated at more than 500 million US$) this seems manageable for the national and regional economies. On the other hand, hard coastline defence and accelerated sea-level rise will increase “coastal squeeze” on the seaward side, endangering important coastal ecosystems such as tidal flats (Wadden Sea), saltmarshes, and dunes. Currently there is no strategy to remedy this increasing ecological vulnerability. --emphasis added

Tom Curtis @ 13
If I am reading you correctly, the rate of sea level rise from 16K to 8K is well documented and therefor possible. I agree with you and also agree that we may be on the front end of another acceleration. Time will tell. And, I agree with you that even with rates of change in the upper bounds of prediction we can easily adapt.

Last time someone prescribed 'adaptation' to sea level rise, we had China building cities out of nothing and Egypt building a seawall from Alexandria to Port Said. It was said to be no problem, they have lots of folks looking for work.

Send the bill to the authors of such comments.

I'd love to hear someone offer a serious counter to the quote in my prior comment. Until then, there's no strategy for this.

scaddenp @ 29 and muon @ 30
We've been adapting to sea level rise since the last Ice Age. According to what I've read on this website, even if we eliminated all FF use we are still in for long-term warming and therefor sea level rise.

So, it does not matter who created the problem - we are going to have to adapt. And, scaddenp, we are all part of the problem.

During the past half century, those places experiencing the greatest SLR are also the same places which have contributed the most CO2. These include the Eastern U.S. and Gulf of Mexico, the East coast of Japan, New Zealand, and the Phillipines (alright, the Phillipinos have not contributed as much). Ironically, those contributing the most CO2, also get to pay for the adaption.

Irrelevant.
- the rise of overpopulated cities with insufficient infrastructure in the vulnerable coastal zone occurred in the last 100 years.
- the interconnection of world financial systems, largely in coastal cities, occurred in the last 20 years
- the proliferation of dangerous weapons available to highly motivated (hungry, frightened, angry, displaced) people -- and a potent demonstration of their effectiveness against affluent, complacent populations -- occurred in the last 10 years

The fact that you cannot offer more than 'we can adapt' indicates that you aren't prepared for serious discussion on this issue. How do you respond to student questions about the likelihood of climate change driving more frequent extreme events -- another Katrina, another Pakistan flood, a continued Sahel drought? Just say adapt? Grow gills?

Ah, irony. Millions will suffer deprivation and disease. Tens of thousands will die each year. Is this your ironic definition of 'also get to pay for the adaption'?

BTW, your short list of 'places which have contributed the most CO2' is grossly incorrect. And if you are trying to isolate SLR effects to specific locations, you are all wet. Example: as the Gulf of Mexico rises, the Louisiana Offshore Oil Port and its terminal at Port Fourchon goes under. That's connected to 50% of US refining capacity. Maybe you were feeling good about not living on the drowning coastline, but this means you won't get to drive much. Or maybe we'll 'just adapt.'

Muon @ 33
Please correct me if I am wrong. Are you saying the fact that we have adapted to SLR since the last ice age is irrevelevant? If so, can you please explain?

Your first bullet may be correct and is a good example of what happened in New Orleans. But, are you trying to connect Katrina to AGW? If so, I need you to provide some evidence. We studied Hurricane Katrina at length and at no times did our resources ever indicate any proven connection to AGW. The effects of Katrin, which was only a Category 3 hurricane, were exacerbated by poorly designed and even more poorly maintained levees and pumping stations. And, you are talking about a city that lies below sea level. The loss of the wetland buffer areas (which is due to man's actions) was also a maor contributor.

And, please tell me that your 3rd bullet is not referencing terrorism. If it is please define.

Pirate - houses go on fire from "natural" causes. Does that mean I have no legal recourse against an arsonist? I am sorry but this seems to be simply a case of being interested in your own rights without consideration for the rights of others, and a refusal to take responsibility for consequence of action (and inaction). Is this really the values that you support?

As to "who is responsible" - then the check the graphic here. Frankly this is "we are all part of the problem" is dead wrong. This is just an attempt at self-justification.

Eric - the places most likely to be affected badly by rising sea level are the great deltas with high population densities, - Mekong, Nile, Ganges, Niger etc. Dont see many of the inhabitants ranking high in the CO2 emission stakes. (The exception would be the Rhine -ie netherlands).

pirate#37: "the fact that we have adapted to SLR since the last ice age is irrevelevant"

It's all about rates of change. Compare the pace of your 'natural cycles' to what we see now.

Look more carefully at the 2nd graph you posted here. In a detail view:

Most of what we call civilization dates back to circa 6000 yrs bp. During that entire time period, SLR was approx 3 meters; a rocking 0.5 mm/year. Now we are measuring upwards of 3 mm/yr. So yes, your statement about the last ice age is irrelevant.

"The loss of the wetland buffer areas (which is due to man's actions) was also a maor contributor."

Once vegetation dies, there is a loss of soil volume due to loss of root turgor and oxidation of root organic matter, which leads to elevation collapse. Revegetation cannot occur because of the low elevation and weak soil strength.

Or due to the combination of subsiding coastline and rising sea level. Tell us how developing countries 'adapt' to bigger storm surges.

"are you trying to connect Katrina to AGW?"

No need. I cited Katrina as an example; pick last year's Queensland storm if you like. And here's a connection between rising sea surface temperature and Atlantic hurricanes.

The record-breaking Atlantic tropical cyclone activity of 2005 followed an active 2004 season, during which Hurricanes Charley, Frances, Ivan and Jeanne all wreaked havoc in Florida. Although sea surface temperatures (SSTs) in the Atlantic had been elevated above the long-term average since 1995... In the aftermath of 2005, modelers began to explore ways to address the possibility that, as long as SSTs remained elevated, hurricane activity and insured losses might also be elevated.

Climate change acts as a threat multiplier for instability in some of the most volatile regions of the world. Projected climate change will seriously exacerbate already marginal living standards in many Asian, African, and Middle Eastern nations, causing widespread political instability and the likelihood of failed states.

The other consequences such as rise in deaths from vector-borne diseases, dislocation due to floods and sea-level rise have been shown as projected economic losses for the years 2025 and 2050. The economic costs of sea-level rise in terms of loss of property along the coastline have also been projected for a 25- and 50-year timescale respectively. The costs arising due to increase in malaria, diarrhoea and leptospirosis outbreaks have been projected till 2050. The conservative estimate of total costs of all these impacts, including the impact of climate change on tourism, are found to be enormous.

EtR - because as temperature warms sealevel will rise and they will get their share. "Recently" I hope means you are thinking "since 1950" - no cherry picks. Those places not where I expect sealevel to rise fastest - just where I expect the effect of sealevel rise to be most severe.

And no, of course I dont expect to stay in their houses and drown. I expect reduced food production from salt incursion and migration into places which are already crowded - unless you are offering a home?

Muoncounter @ 40
A change from 0.5 mm/yr to 3.0 mm/yr may appear to be drastic, but let's look at it realistically. Pull the plug out of your iPod earbuds. The width of that plug is roughly 0.12 inches = 3 mm. That is certainly adaptable by plants, animals, and human animals.

Coastal marshes can change annually from salt to brackish to fresh. So, your statement about saltwater intrusion destroying wetlands is only partially correct. You would need to read more than the abstract in the link provided. The interface between land and sea is dynamic and there is always a battle between the creation and destruction of land.

On the Waccamaw River in coastal SC, where I used to live and still maintain a home, we witnessed a massive saltwater intrusion that killed freshwater species many miles upstream. The cause was an extended drought and not sea level rise. As the drought abated over the next few years, we witnessed a change back to the brackish and freshwater species. The smaller freshwater species recovered more quickly than the larger ones such as bald cypress. This is a nice powerpoint on a Delaware Estuary Study

Also, anthropogenic pressures on tidally influenced freshwater streams and estuaries largely come from urbanization, improper land use practices, impervious cover, dredging and any change to the hydrology of the stream. One of the major problems in the loss of the Louisiana wetlands were the creation of dams, levees and canals which increased the rate of water flow and did not allow the usual sedimentation to occur.

From Louisiana State University "During the last few decades, the human factor in wetland loss has increased drastically. The placement of dams and levees across and along the tributaries and distributaries of the Mississippi River have reduced both the amount and texture of sediment reaching the coast."

[inflamatory snipped]

00

Moderator Response: [Dikran Marsupial] Please stick to the science and leave the moderation to the moderators.

A change from 0.5 mm/yr to 3.0 mm/yr may appear to be drastic, but let's look at it realistically.

You are ignoring the "per year" aspect of a 2.5mm/yr increase.

Ten years, 25 mm. Fifty years, 125 mm.

Beyond this, storm surges and other factors make periodic maximums even larger.

Also, sea level changes are not homogeneous. This is a global average, but individual changes can be much, much greater, due to regional effects.

Places like the Netherlands and New Orleans are also already dangerously below sea level.

Meanwhile, for many ecosystems parts of the world, even this seemingly small change is large. Your provision anecdotal examples of cases where changes are not relevant says nothing about the frequency or importance of cases where it is.

In order to adapt, one must first be aware of the problem. In the case of humans, comments like this are among those that will keep lots of people in the dark.

"On the Waccamaw River in coastal SC, ..."

Your examples reveal nothing more than confirmation bias. Do you not understand that it is the combination of subsidence due to poor coastal land management and the effects of rising sea level (plus increased storm surge) that are the problems? Or that the point of this article was 3mm/yr measurable now, more to come fairly soon?

There is a host of literature detailing the risks of sea level rise; example Dasgupta et al 2007:

Sea-level rise (SLR) due to climate change is a serious global threat: The scientific evidence is now overwhelming. Continued growth of greenhouse gas emissions and associated global warming could well promote SLR of 1 m in this century, and unexpectedly rapid breakup of the Greenland and West Antarctic ice sheets might produce a 3–5 m SLR. ... Our results reveal that tens of millions of people in the developing world are likely to be displaced by SLR within this century; and accompanying economic and ecological damage will be severe for many. At the country level results are extremely skewed, with severe impacts limited to a relatively small number of countries.

This paper explores for the first time the global impacts of extreme sea-level rise, triggered by a hypothetical collapse of the West Antarctic Ice Sheet (WAIS). As the potential contributions remain uncertain, a wide range of scenarios are explored: WAIS contributions to sea-level rise of between 0.5 and 5 m/century. Together with other business-as-usual sea-level contributions, in the worst case this gives an approximately 6-m rise of global-mean sea level from 2030 to 2130. Global exposure to extreme sea-level rise is significant: it is estimated that roughly 400 million people (or about 8% of global population) are threatened by a 5-m rise in sea level, just based on 1995 data.

Muon @ 46
Let me amend my statement based on your version of my statement. "We can and we must adapt to possible changes in sea level."

Both of the references you noted may become real, but it is absolutely not going to happen overnight. It will take decades. These people in the developing world really don't have much to move. As a matter of fact, they've been moving back and forth with shifting land masses ever since the regions were settled. I guess it is hard to feel sorry for an affluent person on Pawleys Island, SC who loses their million dollar vacation home due to shifting sands compared to the millions you reference in your links. I know I don't feel sorry for anyone who builds expensive structures in areas prone to hurricanes, flooding, earthquakes, or landslides. I bet you don't either.

Overpopulation is a real issue in developing countries especially when compared to developed countries. If they choose to live in unstable areas, then I'm not sure what can be done about that.

The point isn't whether any one ecosystem is threatened right now. The point is that there are certainly ecosystems that will be threatened by a 3 mm/yr rise in sea level, if it continues for any length of time, and even more (and sooner) if it accelerates. Hansen makes a decent case for that being a possibility that should be considered, even if any might consider it unlikely.